MAX1000 FPGA UARTs

UARTs are particularly useful for FPGA embedded processors as it quickly becomes very tedious using LEDs for debugging and for program output.  The Elektor 8080 embedded processor experiment 5 requires two UARTs one for terminal I/O and the other for program load and debug statements.

As an introduction to UARTs I used an electronoobs tutorial which provides a clear explanation of the verilog required to send and receive bits.  I used MAX1000 pins A4/B4 to utilise the internal UART for testing.

For the second UART Elektor I used an FTDI RS232 cable attached to pins M2/M1. I could have used any available GPIO and if I wanted I could add more terminals using more FTDIs/GPIOs.

Initially, in Elektor experiments 1 and 2,  executable 8080 C programs are loaded into the image which is downloaded to MAX1000.  Changing a program requires you to compile a program and put the executable in the Quartus project folder then running synthesis and loading using Programmer, which very quickly becomes very tedious.  Elektor experiment 5 uses Processing (a C environment on PC equivalent to arduino) to transmit executable 8080 C programs to MAX1000 via a serial interface.  The interface also provides some basic commands to be be used for debugging.

Our first serial interface (built-in B4/A4) is required for SYSIN/SYSOUT terminal I/O and we use the second one (FTDI M2/M1)  for program loading. [August 2019]